Electrical limit switch

ABSTRACT

An electrical limit switch includes a shaft which is selectively rotated by a switch-actuating rocker arm. A pinion cooperates with a symmetrically biased rack for effecting a centered rest position for the shaft and rocker arm, and a cam is affixed to the shaft to selectively connect and disconnect electrical contacts acting through a plunger linkage. In accordance with other aspects of the present invention, additional plunger-actuating embodiments are provided to effect contact-switching responsive to associated applied mechanical displacements.

United States Patent Dietrich Mar. 14, l 972 [54] ELECTRICAL LIMIT SWITCH 2,390,365 l2/l945 Goff ..200/47 X [72] Inventor: Walter L. Dietrich, Windsor, Conn. 2232 et al [73] Assignee: Arrow-Hart lnc., Hartford, Conn. 3,244,015 1966 Pflfl'iS 2 7 X 3,252,345 5/1966 Russelh. ..200/47 X [221 Flledi July 30,1969 3,412,223 11/1968 Schad ..200/153 (19 x 21 A l. N 846 002 1 pp 0 Primary Examiner-Robert K. Schaefer Assistant Examiner-William J. Smith [52] US. Cl. ..200/47, 200/ l 53 K Attorney-Davis, Hoxie, Faithful] & Hapgood [51] Int. Cl. ..ll0lh 19/32 [58] Field ofSearch ..200/47, 153 K, 153 P, [53 T, [57] ABSTRACT 200/6 A; 74/29 30 An electrical limit switch includes a shaft which is selectively rotated by a switch-actuating rocker arm. A pinion cooperates [56] References Cited with a symmetrically biased rack for effecting a centered rest position for the shaft and rocker arm, and a cam is afiixed to UNITED STATES PATENTS the shaft to selectively connect and disconnect electrical con- 3,317,687 5/1967 Dehn ..200/47 tacts acting through a plunger linkage. g 12/1968 P et 8 2 In accordance with other aspects of the present invention, ad- 6/1970 Games et 0/ 7 ditional plunger-actuating embodiments are provided to effect Boll-V811 et Contact switching responsive to associated pp mechani 3,546,954 12/1970 Ustm ..200/47 ca] disp1acemems 430,054 6/1890 Anderson ZOO/153.16 2,328,266 8/1943 Durbm ..200/47 22 Claims, 11 Drawing Figures 1 I /8 E 35 iii K i 2 2 i ,&*79

PATENTEDMAR 14 I972 SHEET 1 BF 4 WA T R INVENTOR l E L- D/ETR/CH FIG. I

A TTORNE vs ELECTRICAL LIMIT SWITCH This invention relates to electrical switches and, more specifically, to heavy-duty limit switches for selectively actuating switch contacts responsive to preselected applied mechanical displacements.

Electrical limit switches comprise a widely employed class of switching apparatus for selectively completing and/or interrupting one or more electrical connections depending upon the position of a displaceable switch-sensing member.

It is an object of the present invention to provide an improved electrical limit switch.

More specifically, an object of the present invention is the provision of a limit switch which includes sealed switch-actuating and contact assemblies to keep these members free of moisture, waste, corrosive and other foreign matter.

Another object of the present invention is the provision of a limit switch-including apparatus for centering a switch-sensing member to a central rest position.

Yet another object of the present invention is the provision of a limit switch adjustable for clockwise or counterclockwise actuation.

Still another object of the present invention is the provision of plunger operated limit switches which are actuated by applied mechanical displacements parallel or orthogonal to the direction of plunger motion.

These and other objects of the present invention are realized in a specific illustrative limit switch employing a shaft which is selectively rotated by a switch actuating rocker arm. A pinion is mounted upon the shaft and cooperates with a symmetrically spring-biased rack for centering the shaft and rocker arm to a centered rest position.

A cam is concentrically affixed upon the shaft and secured in one of two relative orientations to the pinion. The cam rotates with the shaft when the rocker arm is displaced, and is adapted to selectively actuate switch contacts via two aligned separate abutting plunger assemblies.

For other embodiments of the present invention, the aligned plunger assemblies may be actuated by displacement of switch-sensing members parallel or orthogonal to the direction of motion of the plungers.

A complete understanding of the present invention and of the above and other objects, features, and advantages thereof may be gained from a consideration of the following detailed description of an illustrative embodiment thereof presented hereinbelow in conjunction with the accompanying drawing, in which:

FIG. I is a cross-sectional view of a first specific electrical limit switch which embodies the principles of the present invention;

FIGS. 2A and 2B depict a spring biased rack and pinion switch subassembly for the FIG. 1 switch when a switch rocker arm is centered, and displaced in a clockwise direction, respectively;

FIG. 3 is a cross-sectional view taken at section 3-3 in FIG.

FIG. 4 depicts a spring-biased rack and pinion subassembly adjusted for counterclockwise operation of the FIG. I switch;

FIG. 5 depicts a rack employed in the FIG. 1 limit switch;

FIG. 6 is a cross-sectional view of a second limit switch-actuating arrangement which responds to an applied displacing force coaxial with contact operating plungers shown in FIG. 1;

FIG. 7 depicts in cross section a third limit switch-actuating arrangement which is responsive to an applied tilting displacement ofa sensing member;

FIG. 8 is a cross-sectional view of a fourth limit switch-actuating arrangement adapted to respond to displacements of a sensing member transverse to the direction of motion of a contact-operating plunger assembly;

FIG. 9 is a cross-sectional view taken at section 99' in FIG. 8 depicting the actuating arrangement of FIG. 8 adapted to include latched bistable operating positions; and

FIG. 10 is a bottom view of the actuating arrangement similar to FIG. 8 but adapted to have only one stable, rest posi- (10H.

Referring now to FIGS. 1, 2A and 3, there is shown a first illustrative electrical limit switch which includes an upper housing 12 having a shaft 14 passing therethrough. A rocker arm 28 is secured to one end of the shaft 14, as by a screw 32 which compresses split bottom sections of the arm 28 against each side of the shaft 14. A roller 26 is rotationally secured by a pin 30 to the upper portion of the rocker arm 28.

The upper housing 12 has a laterally projecting collar 15 about one-third of which is cut away as at 17 (see FIG. 3). The shaft passes through opposite sidewalls of the housing and concentrically through the collar 15. A stoppin 3S threaded on one end is threaded into an internally threaded diametrical bore to limit rotation of the rocker arm 28, i.e., the arm 28 is free to rotate in either direction about a central rest position until the pin 35 abuts one edge or the other of the cutaway 17. As more fully discussed hereinafter, the composite limit switch can be adjusted to respond to either clockwise or counterclockwise displacements of the arm 28 by unscrewing the pin 35, rotating the arm 28 and shaft 14 one-half of a revolution, and reinserting the pin 35 in the opposite end of the hole 13.

A pinion 20 is loosely mounted on the shaft 14. Meshing with the pinion are the teeth of a rack 18 which is located in the upper part of the housing I2 in position to be driven to and fro by the pinion. The rack (FIG. 5) has a U-shaped channel in its upper surface which is divided centrally by opposed inward extensions forming in effect a transverse partition 19 having a vertical slot.

To normally center the rack, two compression springs 34 and 36 are positioned in the channel of the rack on opposite sides of the partition with one end of each spring pressing against the partition. The opposite ends of the spring press against the opposite end walls of the housing 12. A fixed pin 16 extends down through the top wall of the housing into the channel of the rack between the springs 34, 36 and into the slot in the partition so that when the rack is moved to the right, its slotted partition compresses the spring 36, while the left spring 34 remains inactive with its right end held by the pin 16 (see FIG. 2B). The opposite occurs when the rack moves to the left.

A cam member, having a cylindrical body 22 and a radially extending cam disc 24 is secured to the shaft 14 by a pin 23 passing diametrically into the shaft 14. The cam body 22 has in one side face recesses 74 and 76 which respectively mate with like-shaped projections 72 and 71 extending from the adjacent side face of the pinion 20. The members 71, 72, 74 and 76 cause the cam and pinion to move together when the shaft 14 is rocked by the arm 28. As discussed below, the switch apparatus is arranged to respond to clockwise or counterclockwise movement of the shaft and rocker arm 28. In FIG. 2A the arrangement is for response to clockwise movement. Reorientation of the cam 22 relative to the pinion 20, as by rotation to seat the projections 71 and 72 in the recesses 74 and 76, respectively, will cause response to counterclockwise rotation.

A separate lower housing 39 which is bolted to the upper housing 12 is provided for the switch contacts and mechanism. To transmit the motion of the cam 24 to the switch contacts, a plunger 40 contacts the cam surface 25 at one end and, at its other end, acts against a second plunger 48 aligned therewith. A compression spring 70 is provided between a lower switchhousing portion 77 and the bottom of the plunger 48 to urge the plungers 40 and 48 upwards towards the cam surface 25. The plunger 40 selectively slides vertically through a bushing 78. Similarly, the plunger 48 slides through a support member 80.

To seal the plungers and switch contacts (described below) from the actuating mechanism and from outside dirt, a double seal is provided comprising a flexible diaphragm 42 of rubber or equivalent material, affixed to the top of the plunger 40. The periphery of this diaphragm is attached to the housing. The second seal 50 is a flexible diaphragm secured to the plunger 48 by an O-ring 82. Its periphery is attached to the support member 80.

Two pairs of stationary electrical contacts 56-58 and 84- 86 are included in the limit switch and electrically connected by conducting metallic sheets to corresponding electrical terminals of any known form (not shown). The switching apparatus also includes two additional bridging contacts 52 and 54 which are electrically connected together, and physically joined by flexible metallic strips 60 and 64 disposed about the plunger 48. Two springlike elements 62 and 66 are connected to the strips 60 and 64, and the elements 52-60-62 and 54-64- 66 serve as butterfly contact bridging arrangements, well known to those skilled in the art, to selectively connect either the contacts 56 and 58 or the contacts 84 and 86. More specifically, the bridging contacts 52 and 54 are urged against the contacts 84 and 86 by the elements 60 and 62, and 64 and 66 when the plunger 48 is biased upward by the spring 70, i.e., when the plunger 40 engages the smaller diameter portion of the cam surface 25. Accordingly, the contacts 84 and 86 are connected while the contacts 56 and 58 are open circuited. Conversely, the bridging contacts 52 and 54 interconnect the contacts 56 and 58 responsive to the plungers 40 and 48 being forced downward when the relatively large diameter portion of the cam surface 25 engages the plunger 40.

The lower housing 39, including the switch contacts 56-58, 6 and the contact-actuating biased plungers 40 and 48 are employed in all composite limit switch embodiments included herein. Additional plunger-displacing (and thereby contact operating) arrangements are presented hereinbelow to respond to varying predetermined applied mechanical displacements. Such actuating arrangements are in every case attached to the lower housing (e.g., by bolts which are secured in threaded apertures in the lower housing 39) in the same manner as the upper housing 12 including the rotary switchactuating apparatus here being considered.

With the above structure for the FIG. 1 limit switch construction in mind, an illustrative sequence of operation for the switch of FIGS. l-3 will now be described. The rack 18 is biased midway across the switch-housing 12 by the two compression springs 34 and 36 acting against the upper rack portion 19 when no mechanical force is applied to the roller 26 on the rocker arm 28. This central positioning of the rack, in turn, centers the rocker arm 28 acting through a linkage train comprising the pinion 20, the cam body portion 22 and the shaft 14.

It is observed that the rack 18, and therefore also the rocker arm 28, will be centered notwithstanding any dissimilarity in the characteristics of the springs 34 and 36, and independent of the force of gravity acting on the rocker arm 28 if the switch is mounted other than vertically. If the rack should become spuriously displaced from center for any reason, one spring 34 or 36 will become compressed while the other is held by the pin 16, and the compressed spring 34 or 36 will quickly expand and return the rack 18 (and thereby also arm 28) to its centered position. The compressed spring 34 or 36 acts merely against the very small gravity forces and the inertia of the structure mounted on the shaft 14, and is not opposed by the companion spring.

With the rack 18 and arm 28 centered as shown in FIG. 2A, the plunger 40 rests against the small diameter section of the cam surface 25. Accordingly, the plunger 48 is maintained in a raised position by the spring 70. The contacts 84 and 86 are thus normally connected and the contacts 56 and 58 not connected.

When the rocker arm 28 is rotated clockwise, the cam 22- 24 and the pinion 20 are similarly rotated clockwise, to the position in FIG. 2B. The raised portion 25 of the cam surface forces the plungers 40 and 48 downward, thereby compressing the spring 70. The bridging contacts 52 and 54 switch to the contacts 56 and 58 when the plunger 48 is so displaced, and the contacts 56 and 58 are thus connected while the contacts 84 and 86 become disconnected. This electrical state persists as long as the arm 28 remains rotated.

When the mechanical force is removed from the arm 28, the compressed spring 36 (FIG. 2B) forces the rack 18 to its centered position (FIG. 2A). The compressed spring 70 lifts the plungers 48 and 40, and the contacts 56 and 58, and 84 and 86 are reset to their initiai state. This completes a full cycle of operation for the electrical limit switch of FIGS. 1-3.

The switch shown in the drawings may alternatively be made responsive to counterclockwise rotations of the rocker arm 28. To effect this mode of operation, the setscrew 35 is removed and the shaft 14 pushed towards the rear of the upper housing 12 through a space 79. This separates the pinion projections 71 and 72 from the cam recesses 74 and 76 as the cam moves away from the pinion 20 with the shaft 14. The shaft 14 is next rotated 180 and then pulled forward such that the pinion projections 71 and 72 fit within the alternate recesses 74 and 76 in the cam body portion 22. The setscrew 35 is then replaced in the threaded shafthole 13 through the gap in the housing projection 39. Finally, the arm 28 is rotated 180 degrees on the shaft 14, as by loosening and retightening the screw 32.

The cam arrangement effected by the above operations is shown in FIG. 4. A counterclockwise rotation of the arm 28 and shaft 14 will depress the plungers 40 and 48 to actuate the switch contacts, while a clockwise rotation of the shaft 14 will have no such effect. The above conversion steps, if carried on again, will return the switch to clockwise operation, and so forth.

The above-considered limit switch is thus adjustable to respond to clockwise or counterclockwise mechanical displacements from a stable center rest position for actuating electrical contacts.

A second illustrative contact-actuating embodiment is shown in FIG. 6, and includes a housing adapted for attachment to the lower switch housing 39 of FIG. 1 as discussed above. Accordingly, only the uppermost portion of the housing 39 is shown in FIG. 6. This actuator embodiment is employed to render the limit switch contacts responsive to an applied displacement of a sensing member in a direction coaxial with the plungers 40 and 48 for directly pushing the plungers downward.

To couple the applied force (displacement) to the plunger 40, a displacement-sensing member, e.g., a roller 114 is secured to a push rod 102, as by a pin 115. The push rod 102 is mounted in a sleeve bushing 103 to vertically slide within the housing 100. The terms vertical" and horizontal as used herein refer to the switch orientation shown in the drawing. The switches may be employed in any desired orientation.

To prevent damage to the composite switch by excessive displacement of the roller 114 and rod 102, the rod 102 is coupled to the upper plunger 40 by an overtravel linkage comprising a ram disposed within a cavity 109 in the rod 102, a plunger drive member 1 11, and an overtravel spring 1 12 within the drive member 1 11 which interconnects the elements 110 and 111.

The lower portion of the push rod 102 slides about the exterior of the drive member 111 which is partially located within the cavity 109, and the rod includes a shoulder portion 108 which abuts against the bottom of the bushing 103 to limit upward travel of the push rod 102. Finally, a flexible seal 104 is provided between the push rod 102 and housing 100 to keep the switch-actuating parts free from foreign matter.

The push rod 102 is normally biased upward in FIG. 6 by the spring '70 (FIG. 1) which acts through the pistons 48 and 40, the drive member 111, the overtravel spring 112 and the ram 114.

The contacts 56-58 and 84-86 switch operative states when an external force pushes the roller 114 and the push rod 102 downward. This forces the ram 110 downward, thereby causing the spring 112 and the drive member 111 to force the plungers 40 and 48 downward hence operating the switch con tacts. When the sensing roller 114 is released, the switch returns to its normal rest position.

Should the push rod 102 be driven downward an excessive amount, the rod 102 would slide down about the periphery of the drive member 111 (which abuts against the top of the lower housing 39 when the switch is operated). The excessive travel of the ram 110 compresses the overtravel spring 112 which thus contracts to absorb the excessive push rod displacement. Thus, no switch element is damaged by the abnormal movement of the rod 102.

A piston-actuating arrangement similar to the FIG. 6 embodiment is illustrated in FIG. 7, and includes a housing 121 which is fastened to the lower switchhousing 39. The switch is operated by pushing a lever 127 downward, or by tilting the lever 127 in any direction. The lever 127 may be formed of one continuous element, or of spaced elements connected by a coiled spring as shown.

To couple the input lever displacement to the contact-actuating plungers, the lever 127 is connected to the ball member of a ball joint comprising a hemispherical ball 119 which is mounted for rotation within a spherical socket aperture 122 in the housing 121. A push rod 120 is included within the housing 121 and mounted to slide vertically within the housing. When the lever 127 is pushed downward, the ball 119 pushes the rod 120 downward against the resistance of a return spring 124.

Similarly, the push rod 120 is forced downward when the lever 127 is rotated by a force or mechanical displacement orthogonal or at another angle to the vertical axis in FIG. 7. The displaced lever 127 rotates the ball 119 within the socket 122. One portion of the rotated ball 119 is thus moved downward, thereby forcing the abutting push rod 120 downward.

An overtravel linkage, identical in construction and operation to the like-numbered linkage in the switch actuator embodiment of FIG. 6, operates the switch contacts 56-58 and in the lower housing 39 responsive to a downward travel of the push rod 102. In brief, rotation or depression of the lever 127 moves at least a portion of the ball 119 downward, thereby forcing the push rod 120 downward and compressing the return spring 124. This motion of the rod 120 moves the overtravel ram 110 downward, thereby compressing the overtravel spring 112 which urges the drive element 111 downward, thus actuating the plunger 40 (and 48) and switching the contacts.

When the actuating force is removed from the lever 127, the ball and lever are returned to their normal position by the return spring 124 hence releasing the contacts.

A switch-actuating apparatus of the side push type is shown in cross section in FIG. 8 and includes an actuator housing 130 mounted atop the lower switch contact housing 39. The housing 130 includes a central bore 131 having a push rod 137 therein. The push rod 137 is adapted to slide through the bore, as through sleeve bushings 142 and 143.

The housing 130 includes a groove 133 adjoining the bore 131, and a stop 132 is mounted on the push rod 137 and located for movement within the groove 133. The travel of the stop 132 within the groove 133 defines the limit of horizontal motion of the rod 137 and, moreover, the stop 132 prevents rotation of the push rod 137 within the bore 133.

For purposes of displacing the contact'operating plungers 40 and 48, the push rod 137 includes apparatus comprising operative bottom cam surfaces 135 and 136, and a transitional surface 134. A springlike drive bracket 138 is secured to the frame 130, and biases a cam follower 139 upward against the cam surfaces 134-136. Seals 140 are provided at either end of the actuator housing 130 between the housing and the push rod 137 to keep waste material and the like from the interior actuator components.

When the cam surface 136 is disposed above the follower 139 (corresponding to the push rod 137 being its leftmost position with the stop 132 against the left wall of the groove 133), the drive bracket 138 biases the follower 139 upward and the bracket 138 does not engage the plunger 40. Accordingly, the switch resides in its normal, rest position.

The switch contacts 56 and 58, and 84 and 86 are operated by moving the push rod 137 to the right such that the cam surface 135 depresses the follower 139 and the drive 138 downward, thereby depressing the contact actuating plunger 40.

The switch assembly of FIG. 8 can be made to operate in either a maintained, bistable latched mode, or in a nonlatched mode. For maintained contact bistable operation, detent apparatus (FIG. 9) is provided to maintain the push rod 137 in either of two stable positions wherein one of the cam surfaces 135 or 136 is located above the follower 139. The detent structure may advantageously comprise two pairs of shallow spherical grooves 141 on either side of the push rod 137, with the grooves being spaced for proper positioning of the cam surfaces 135 and 136 over the follower 139. Two balls 142 are placed on either side of the push rod 137 and biased toward,

the rod by springs 146. The push rod 137 is alternately latched in its two stable positions as the balls 142 seat in the two pairs of spaced spherical recesses 141. The detent assembly is secured to the composite actuator assembly by a bottom plate 144 which may also serve to carry the pivoted drive 138.

A nonlatching actuator assembly is shown in bottom view in FIG. 10 wherein equivalent parts have similar reference numerals. A crossbar plate 147 is secured to the push rod 137a. The plate 147 is biased to the right by two springs 148 which have one end pressing against it and have their other ends in contact with the housing a.

The composite switch of FIG. 10 is operated by moving the push rod 137a horizontally to actuate the plungers 40 and 48 in the manner discussed above via the cam surface 135, the follower 139 and the drive 138, while compressing the springs 148. When the rod 137a is released, the springs 148 expand, and act against the crossbar plate 147 to return the push rod 1370 to its normal position.

It is to be understood that the above-described arrangements are only illustrative of the instant switching arrangement. Numerous adaptations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the present invention. For example, any number of contact groupings may be included in the limit switch and made responsive to movement of the plunger 48.

What is claimed is:

1. In combination in a limit switch, a rockable-actuating shaft, a pinion on said shaft, a rack meshing with said pinion driven thereby and adapted for movement in first and second directions, biasing means acting against movement of said rack in either direction, cam means on said shaft, switch contact means, and contact actuating means engaged and operated by said cam means.

2. A combination as in claim 1 further comprising a housing, a spring stop on said housing, said rack including extension means adapted to move past said spring stop, and wherein said biasing means comprises first and second springs each engaging at one extremity with said housing and at their other extremity with said spring stop and said extension means.

3. A combination as in claim 1 wherein said contact-actuating means includes plunger means, spring-biasing means for urging one extremity of said plunger means into engagement with said cam means, and means responsive to the position of said plunger means for selectively actuating said contact means.

4. A combination as in claim 3 wherein said plunger means includes at least two communicating aligned plungers, and sealing means connected to at least one of said plungers.

5. A combination as in claim 3 wherein the movable elements of said contact means are butterfly members.

6. A combination as in claim 1 having means for selectively adjusting said cam means to operate said contact means on initial movement in either clockwise or counterclockwise direction.

7. A combination as in claim 6 wherein said cam-adjusting means includes means for securing said cam means in a selected one of a plurality of possible positions relative to said pinion.

8. A combination as in claim 7 further comprising a housing, a spring stop on said housing, said rack including extension means adapted to move past said spring stop, and wherein said biasing means comprises first and second springs each engaging at one extremity with said housing and at its other extremity with said spring stop and said extension means.

9. A combination as in claim 8 further comprising a projection on said housing, said projection having a vacated segment, a hole in said shaft, and pin means insertable in said hole in said shaft.

10. A combination as in claim 9 further comprising a rocker arm, and means for selectively positioning and securing said rocker arm to said shaft.

11. A combination as in claim 10 wherein said contact-actuating means includes plunger means, spring-biasing means for urging one extremity of said plunger means into engagement with said cam means, and means responsive to the position of said plunger means for selectively actuating said contact means.

12. A limit switch having fixed and movable contacts and control mechanism comprising a rockable shaft, a gear on said shaft, a rack having teeth meshing with said gear, projection means on said rack, a pair of identical coil-compression springs each fixedly anchored at their opposite ends and each engageable at their adjacent ends by said projection means, a stationary member also engageable by said adjacent ends of said springs when said rack is centered, a cam on said shaft, and a switch-operating member operated by said cam to cause engagement and disengagement of said contacts.

13. In combination in a limit switch, housing means, contact-operating plunger means within said housing means and adapted for linear sliding motion in said housing means, said plunger means including first and second abutting aligned plunger members, spring means for mechanically biasing said plunger means, electrical contact means connected to said second plunger member and operable in response to the movement of said plunger means, a sealed switch compartment enclosing said second plunger member and said contact means and said plunger-biasing spring means, and switch-actuating means including a housing, a push rod slidably mounted in said housing, an external impetus sensing means mechanically coupled to said push rod, and overtravel means for selectively displacing said first and second plunger members and compressing said biasing spring means thereby operating said contact means, said overtravel means including a ram contacting said push rod, drive means contiguous to said first plunger member, and an overtravel spring connecting said ram and said drive means.

14. A combination as in claim 13 wherein said actuatorsensing means comprises means at one end of said push rod, adapted to respond to an external actuation directed along said push rod.

15. A combination as in claim 13 further comprising ball joint means including a socket and a ball member intermediate said push rod and said housing, and wherein said sensing means comprises lever means responsive to external actuation for rotating said ball within said socket.

16. A combination as in claim 15 further comprising return spring means for biasing said push rod away from said first plunger member.

17. A combination as in claim 13 wherein said actuating means includes a housing having a rotatably mounted shaft therein, wherein said sensing means includes a rocker arm for selectively rotating said shaft, and wherein said plunger displacing means includes cam means mounted on said shaft, said actuating means further comprising spring biased rack and pinion means for centering said rocker arm to a rest position.

18. In combination in a limit switch, housing means, con tact-operating plunger means within said housing means and adapted for linear sliding motion in said housing means, said plunger means including first and second abutting aligned plunger members, spring means for mechanically biasing said plunger means, electrical contact means connected to said second plunger member and operable in response to the movement of said plunger means, first sealing means arranged circumjacent the periphery of said first plunger member and mechanically coupled to said housing means for sealing said first plunger member to said housing means, said first sealing means arranged for movement with said first plunger member,

a switch compartment in said housing means enclosin said second plunger member and said contact means an said plunger-biasing spring means, said switch compartment including second sealing means arranged circumjacent the periphery of said second plunger member for sealing said second plunger member within said switch compartment, said second sealing means arranged for movement with said second plunger member, switch-actuating means including external impetus sensing means, and plunger-abutting means in abutting contact with said first plunger member and responsive to a predetermined displacement of said sensing means for displacing said first and second plunger members and compressing said biasing means thereby operating said contacts.

19. A combination as in claim 18 wherein said actuating means includes a housing having a bore orthogonal to the direction of sliding displacement of said plunger members, a push rod in said bore adapted to selectively slide therein, cam means on said push rod, a cam follower, means for biasing said follower against said push rod cam means, said plunger abutting means being responsive to the position of said cam follower for selectively displacing said first plunger member.

20. A combination as in claim 19 further comprising pin and groove means in said housing along said bore, limiting axial and rotational movement of said rod relative to said bore.

21. A combination as in claim 20 further comprising detent means for operating said actuating means in a bistable mode, said detent means including at least one spherical indentation on said push rod, a ball, and spring means for selectively seating said ball within said indentation.

22. A combination as in claim 20 further comprising plate means affixed to said push rod, and additional spring means bearing against said plate means for biasing said push rod to a rest position. 

1. In combination in a limit switch, a rockable-actuating shaft, a pinion on said shaft, a rack meshing with said pinion driven thereby and adapted for movement in first and second directions, biasing means acting against movement of said rack in either direction, cam means on said shaft, switch contact means, and contact actuating means engaged and operated by said cam means.
 2. A combination as in claim 1 further comprising a housing, a spring stop on said housing, said rack including extension means adapted to move past said spring stop, and wherein said biasing means comprises first and second springs each engaging at one extremity with said housing and at their other extremity with said spring stop and said extension means.
 3. A combination as in claim 1 wherein said contact-actuating means includes plunger means, spring-biasing means for urging one extremity of said plunger means into engagement with said cam means, and means responsive to the position of said plunger means for selectively actuating said contact means.
 4. A combination as in claim 3 wherein said plunger means includes at least two communicating aligned plungers, and sealing means connected to at least one of said plungers.
 5. A combination as in claim 3 wherein the movable elements of said contact means are butterfly members.
 6. A combination as in claim 1 having means for selectively adjusting said cam means to operate said contact means on initial movement in either clockwise or counterclockwise direction.
 7. A combination as in claim 6 wherein said cam-adjusting means includes means for securing said cam means in a selected one of a plurality of possible positions relative to said pinion.
 8. A combination as in claim 7 further comprising a housing, a spring stop on said housing, said rack including extension means adapted to move past said spring stop, and wherein said biasing means comprises first and second springs each engaging at one extremity with said housing and at its other extremity with said spring stop and said extension means.
 9. A combination as in claim 8 further comprising a projection on said housing, said projection having a vacated segment, a hole in said shaft, and pin means insertable in said hole in said shaft.
 10. A combination as in claim 9 further comprising a rocker arm, and means for selectively positioning and securing said rocker arm to said shaft.
 11. A combination as in claim 10 wherein said contact-actuating means includes plunger means, spring-biasing means for urging one extremity of said plunger means into engagement with said cam means, and means responsive to the position of said plunger means for selectively actuating said contact means.
 12. A limit switch having fixed and movable contacts and control mechanism comprising a rockable shaft, a gear on said shaft, a rack having teeth meshing with said gear, projection means on said rack, a pair of identical coil-compression springs each fixedly anchored at their opposite ends and each engageable at their adjacent ends by said projection means, a stationary member also engageable by said adjacent ends of said springs when said rack is centered, a cam on said shaft, and a switch-operating member operated by said cam to cause engagement and disengagement of said contacts.
 13. In combination in a limit switch, housing means, contact-operating plunger means within said housing means and adapted for linear sliding motion in said housing means, said plunger means including first and second abutting aligned plunger members, spring means for mechanically biasing said plunger means, electrical coNtact means connected to said second plunger member and operable in response to the movement of said plunger means, a sealed switch compartment enclosing said second plunger member and said contact means and said plunger-biasing spring means, and switch-actuating means including a housing, a push rod slidably mounted in said housing, an external impetus sensing means mechanically coupled to said push rod, and overtravel means for selectively displacing said first and second plunger members and compressing said biasing spring means thereby operating said contact means, said overtravel means including a ram contacting said push rod, drive means contiguous to said first plunger member, and an overtravel spring connecting said ram and said drive means.
 14. A combination as in claim 13 wherein said actuator-sensing means comprises means at one end of said push rod, adapted to respond to an external actuation directed along said push rod.
 15. A combination as in claim 13 further comprising ball joint means including a socket and a ball member intermediate said push rod and said housing, and wherein said sensing means comprises lever means responsive to external actuation for rotating said ball within said socket.
 16. A combination as in claim 15 further comprising return spring means for biasing said push rod away from said first plunger member.
 17. A combination as in claim 13 wherein said actuating means includes a housing having a rotatably mounted shaft therein, wherein said sensing means includes a rocker arm for selectively rotating said shaft, and wherein said plunger displacing means includes cam means mounted on said shaft, said actuating means further comprising spring biased rack and pinion means for centering said rocker arm to a rest position.
 18. In combination in a limit switch, housing means, contact-operating plunger means within said housing means and adapted for linear sliding motion in said housing means, said plunger means including first and second abutting aligned plunger members, spring means for mechanically biasing said plunger means, electrical contact means connected to said second plunger member and operable in response to the movement of said plunger means, first sealing means arranged circumjacent the periphery of said first plunger member and mechanically coupled to said housing means for sealing said first plunger member to said housing means, said first sealing means arranged for movement with said first plunger member, a switch compartment in said housing means enclosing said second plunger member and said contact means and said plunger-biasing spring means, said switch compartment including second sealing means arranged circumjacent the periphery of said second plunger member for sealing said second plunger member within said switch compartment, said second sealing means arranged for movement with said second plunger member, switch-actuating means including external impetus sensing means, and plunger-abutting means in abutting contact with said first plunger member and responsive to a predetermined displacement of said sensing means for displacing said first and second plunger members and compressing said biasing means thereby operating said contacts.
 19. A combination as in claim 18 wherein said actuating means includes a housing having a bore orthogonal to the direction of sliding displacement of said plunger members, a push rod in said bore adapted to selectively slide therein, cam means on said push rod, a cam follower, means for biasing said follower against said push rod cam means, said plunger abutting means being responsive to the position of said cam follower for selectively displacing said first plunger member.
 20. A combination as in claim 19 further comprising pin and groove means in said housing along said bore, limiting axial and rotational movement of said rod relative to said bore.
 21. A combination as in claim 20 further comprising detent means for operating said actuating means in a bistable mode, said dEtent means including at least one spherical indentation on said push rod, a ball, and spring means for selectively seating said ball within said indentation.
 22. A combination as in claim 20 further comprising plate means affixed to said push rod, and additional spring means bearing against said plate means for biasing said push rod to a rest position. 